1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) element, a display having a high definition and a method for manufacturing thereof. In particular, the present invention relates to a method for manufacturing a display having a high definition by printing an ink material on a product to be printed such as a substrate for manufacturing precision parts so as to form a pattern by a printing method.
2. Description of the Related Art
Generally, an organic EL element has an organic luminescent layer having an organic luminous material between two electrode substrates facing each other. By applying a voltage to an organic luminescent layer, an organic EL element emits light. In order to emit light efficiently, it is important to control the thickness of the organic luminescent layer. For example, it is necessary to make a thin film with a thickness of about 100 nm. Moreover, patterning with a high definition is required when a display is manufactured.
As an organic luminous material which is formed on a substrate or the like, a low-molecular material and a high-molecular material can be used. In general, the thin film of a low-molecular material can be formed by a resistance heating deposition method (a vacuum evaporation method) or the like on a substrate, and is patterned using a mask with a fine pattern at this time. However, there is a problem that the larger a substrate becomes, the more difficult it is to obtain a patterning accuracy in this method.
On the other hand, as a process of pattering an organic luminescent layer in order to manufacture a full colored display using a high-molecular luminous material, a method for forming a pattern by an ink jet method and a method for forming a pattern using a printing plate are proposed.
The method for forming a pattern by an ink jet method includes discharging a luminescent layer material which was dissolved in a solvent on a substrate from an ink jet nozzle. Then, a predetermined pattern is obtained by drying the material on the substrate. (Patent Document 1) However, an ink spreads in a circular state at the time of dropping on a substrate, because an ink droplet discharged from the nozzle is spherical. Therefore, there is a problem in that a linear pattern cannot be obtained, because the shape of the formed pattern lacks linearity or the accuracy of the point where the ink droplet is dropped is poor.
On the other hand, for example, a method for forming a linear pattern by the following processes is disclosed (Patent Document 2): a bank is formed on a substrate using a material having an ink-repellent property by a photolithography method or the like; thereafter, an ink droplet is dropped on the substrate and the ink is repelled on the bank portion and a linear pattern is formed. However, when the ink repelled on the bank portion returns inside a pixel, the ink builds up in the pixel. Thereby there remains a problem in that irregularity of film thickness of an organic luminescent layer inside a pixel occurs.
Then, instead of a low-molecular material, patterning by a printing method using an ink which was made by a high-molecular organic material dissolved or dispersed in a solvent, is proposed. As a printing method, a relief printing method, a reverse type printing method or a screen printing method can be exemplified. Especially, relief printing is superior in terms of accuracy of a pattern formation and evenness of film thickness. Thereby, relief printing is suitable for a method for manufacturing an organic electroluminescence element performed by a printing method.
Furthermore, a method such as a gravure printing method in which a hard plate such as a printing plate made of a metal or the like is used is inappropriate among various printing methods, because an organic EL element and a display uses a glass substrate as a substrate in many cases. Therefore, a printing method which uses a printing plate made of rubber having elasticity, an offset printing method which uses a printing blanket made of rubber or a relief printing method which uses a photosensitive resin plate including rubber which has elasticity or including another resist as a main component can be adopted as an appropriate printing method. In an actual case, as an approach of these printing methods, a method for printing a pattern by an offset printing method and a method for printing a pattern by a relief printing method are proposed. (Patent Documents 3 and 4)
However, a formation of an organic luminescent layer by a printing method is significantly influenced by wetting properties of the surface of an area on which the organic luminescent layer is formed. Therefore, in the case where a layer located just under the organic luminescent layer (the layer is defined as an under-layer) is formed only within a pixel on a partition wall substrate as in the past, there was a problem in that the thickness of an organic luminescent layer differed, because wetting properties of the upper surface of a partition wall which is not printed and located around pixels and wetting properties within a pixel were different.
The present invention is practiced to solve this problem. The purpose of the present invention is to provide a method for manufacturing an organic EL element without defect and irregularity by forming the film of the organic luminescent layer uniformly at the time of forming the film of an organic luminescent layer.    Patent Document 1: JP-A-H10-12377    Patent Document 2: JP-A-2002-305077    Patent Document 3: JP-A-2001-93668    Patent Document 4: JP-A-2001-155858